Polychloroprene elastomer

ABSTRACT

A polychloroprene elastomer prepared by blending a toluene insoluble gel polymer, obtained by polymerizing chloroprene or a mixture of chloroprene with at least one copolymerizable monomer, with a toluene soluble sol polymer obtained by polymerizing chloroprene or a mixture of chloroprene with at least one copolymerizable monomer, wherein the cross-linking density of the elastomer is at least 2.4 X 10 6.

United States Patent 1 Kitagawa et al. 51 Jan. 30, 1973 [54] [56] References Cited [75] Inventors: Chojiro Kilagawa; Ichi o Fuku0ka, KT? both of Tokyo; Takashi Kadowaki, UNI D ST S ATENTS NiShi Kubiki-gun, Niigata; Shoji 3,042,652 7/1962 Pariser et al ..'...260/890 3,147,317 9/1964 Jungk et al. ....260/890 f a z gf' g'l f gg 'gzg zg 3,261,888 7/1966 Cornell et al ..260/877 Nishi-Kubiki-gun, Niigata, all of FOREIGN PATENTS OR APPLlCATlONS Japan 799,043 7/1952 Great Britain ..260/4 [73] Assignee: Denki Kagaku Kogyo Kabushiki 851,491 10/1960 Great Britain ....260/894 Kaisha, Tokyo, Japan 853,640 11/1960 Great Britain ..260/41 Filed: 19, 1968 Primary Examiner-Samuel H. Blech [21] A'ppL No; 753,765 AttorneySughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT [52] 11.8. C1... 260/890, 260/297 D, 260/33.6 A,

A polychloroprene elastomer prepared by blending a f gg g gg toluene insoluble gel polymer, obtained by polymerizl l g ing chloroprene or a mixture of chloroprene with at 51 Int Cl Cost least one copolymerizable monomer, with a toluene {58; Fie f 83 5 86 3 soluble sol polymer obtained by polymerizing chloroprene or a mixture of chloroprene with at least one copolymerizable monomer, wherein the cross; linking density of the elastomer is at least 2.4 X 10".

7 Claims, No Drawings POLYCHLOROPRENE ELASTOMER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a polychloroprene elastomer having excellent extrusion and molding pro perties.

2. Description of the Prior Art The term polychloroprene elastomer or chloropreneas used herein refers to polymers of 2- chloro-l ,3-butadiene or copolymers of 2-chloro-l,3- butadiene with one or more copolymerizable monomers.

Ordinary polychloroprene elastomers do not possess satisfactory processability characteristics especially for extrusion molding processes. Generally, it is not characterized by reduced die swell on extrusion through the rolls of the extrusion machines, by resistance to deformation, by smoothness of surface of extruded products, high velocity of extrusion and other factors as would be desirable. Accordingly, it is difficult to fabricate polychloroprene elastomers into shaped articles having complicated contours with any degree of precision by extrusion or by calendering. That is to say, that when manufacturing extruded products having a complicated figure and some resiliency, certain defects appear, namely, deformation, dimension changes, surface roughness, edge napping and the like.

It is an object of the present invention to provide a polychloroprene elastomer which-is free from such defects and which is characterized by an improved processability, and excellent extrusion and molding properties. In more detail, the object ofthe present invention is to provide a polychloroprene elastomer which has excellent extrusion and molding properties as well as other improved processing properties such that it can be fabricated at a high extrusion rate into a smooth-surfaced extruded product which is free from any deformation or warp even though the product has a complicated cross-section.

SUMMARY OF THE INVENTION The present invention. comprises preparing a polychloroprene elastomer byblending a crosslinked toluene-insoluble gel-like polychloroprene (hereinafter referred to as the gel polymer), obtained by polymerizing chloroprene in the presence of a crosslinking agent, with a toluene-soluble sol-like polychloroprene (hereinafter referred to as sol polymer), obtained by ordinary polymerization procedures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS crosslinking agent such as glycol dimethacrylates of the formula wherein n is an integer of from 1 to 8, or

wherein n is an integer of from 2 to 4. Examples of suitable crosslinking agents include ethylene glycol dimethacrylate (EDMA), trimethylene glycol dimethacrylate, tetrarnethylane glycol dimethacrylate (TDMA), diethylene glycol dimethacrylate (DEDMA), triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate (TEDMA) and the like; and divinylbenzene, divinyl ether, diallyl phthalate, divinylsulfone and the like. The excellent extrusion and molding properties of the elastomer of the present invention are obtainable by the use of a highly crosslinked gel polymer having a crosslinking density of at least 2.4 X 10. If the density is less than 2.4 X 10', the die swelling on extrusion will increase, the extrusion rate will decrease, the surface smoothness of the extruded product will be lost and, thus, the material will be poorly extruded. The crosslinking density of gel polymer depends on the type and quantity of crosslinking agent used, the degree of monomer to polymer conversion and other factors and, therefore, the desired value is obtainable by properly adjusting these factors.

The swelling index and crosslinking density of the crosslinked gel polymer are determined in the following manner: The weight Wa of a sample is weighed by means of a chemical balance and the sample is soaked in about cc of toluene contained in a stoppered 100 cc measuring flask. The container is allowed to stand in a thermostat controlled bath of 30C.After reaching swelling equilibrium, the sample is removed from the toluene, lightly wiped with filter paper, and

quickly weighed. The weight (WB) after swelling was noted and the swelling index (Q) was calculated by the equation where P, is the density (g/cc) of gel chloroprene, P is the density (g/cc) of toluene. The crosslinking density 7 is calculated from the value of swelling index by the P. J. Flory and A.M. Bueches equation where V is the volume fraction of solvent toluene, V is the volume fraction of polychloroprene in the swollen gel and ,u is interaction coefficient between polychloroprene and solvent.

The sol polymer used in the present invention may be obtained by polymerizing chloroprene or a mixture of chloroprene with small amounts of one or more copolymerizable monomers in the presence of an aliphatic mercaptan such as n-dodecylmercaptan. The resulting polymer is substantially gel-free and has a Mooney viscosity (M1 at 100C. of at least 15.

In the present invention there may be used as a comonomer copolymerizable with chloroprene, e.g., styrene, vinyltoluene, butadiene, isoprene 2,3- dichlorobutadien'e-l,3, methyl vinyl ketone, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and acrylonitrile.

The gel polymer and sol polymer thus obtained are blended in the form of a latex in the proportion as mentioned above and the mixture is, isolated by freeze coagulation or by similar conventional techniques or by drum drying to obtain a polychloroprene elastomer having aMooney viscosity (ML, at 100C. of 30 to 70, preferably of 40 to 60.

The chloroprene elastomer thus obtained is thixotropic namely, when the elastomer is directly dissolved in benzene only the sol component dissolves and the gel component remains undissolved, when the elastomer is dissolved in benzene after mastication on a roll it dissolves entirely providing a turbid benzene solution which insolubilizes again after a few hours when allowed to stand still at room temperature. The gel polymer by itself is not solubilized by mastication, and this is a peculiar property obtained by blending with a low molecular sol polymer. All gel polymers do not exhibit such property when blended with a sol polymer, for instance, a gel polymer prepared by treating a chloroprene rubber with a peroxide will not exhibit such property.

The greatest characteristic of the rubber obtained by blending a gel polymer with a sol polymer in accordance with the present invention is the thixotropic property as mentioned above. It seems that the excellent extrusion molding property is attributable to this peculiar property since the low molecular sol polymer acts as a plasticizer on extrusion and the thixotropic gel polymer acts to prevent deformation, shrinkage and swelling. As a result of the interaction of the two polymers, the elastomer of the present invention exhibits good flow properties and good processability on extrusion and provides a good extruded product having a reduced deformation and die swelling tendency.

The present invention will now be illustrated by the following example which is not intended to be limiting in any manner. All parts are by weight.

EXAMPLE A. Preparation of sol polymer A polymerization mixture of the following recipe was charged into a stirred jacketed polymerization vessel and gradually heated, with stirring, to 40C. over a period of one hour. A mixed aqueous solution of 0.25

percent of potassium persulfate and 0.025 percent of sodium anthraquinone-B-sulfonate was added to the mixture as a polymerization catalyst. Polymerization was continued to a predetermined conversion.

Chloroprene -100 (parts) Other monomer 5-0 Disproportionated rosin 4 n-Dodecylmercaptan 0.3 Formaldehyde-sodium naphthalene sulfonate condensation product 0.8

Sodium hydroxide 0.8

Water 150 Chloroprene 98 -l00 (parts) Other monomer 2 0 Disproportionated rosin 3.5 n-Dodecylmercaptan 0.2 0.35 Forrnaldehydesodium naphthalene sulfonate condensation product 0.8

Sodium hydroxide 0.8 Crosslinking agent 3 7 Water 150 C. Blend of sol polymer and gel polymer The sol polymer latex and gel polymer latex thus ob tained were mixed together in a latex state to a predetermined proportion, coagulated on the surface of a rotary drum through which was circulated a brine at a temperature of -20 to l0C. The resulting film was washed with water and dried at 100C. to C. to obtain a blend. The polymer blend thus obtained was compounded in accordance with the following recipe.

Polymer blend I 100 (parts) Phenyl-a-naphthylamine 1.0 Magnesium oxide 4.0 Zinc oxide 5.0 Z-Mercaptoimidazoline 0.35

The compound thus formed was extruded by means of a Koka-type flow tester and, thereby, the extrusion rate and the die swelling (ratio of the average outer diameter of the extruded product to the diameter of the extrusion die) were measured. The results were summarized in Table l.

The test conditions by the Koka-type flow tester were as follows:

Die l.0mm 1.0mm Load 60 Kg/cm Temperature 100C.

For comparison, a gel polymer of crosslinking density, of 0.6 X 10 was obtained in the same manner as in the specimen E-9 in the Table 1, except that polymerization was stopped at a conversion of 70 percent and was subjected to the same test. In this case, the extrusion rate was 9.4 X 10' cc/sec., the die swelling was 2.05. The resulting surface smoothness wherein n is an integer of from 2 to 4, divinylbenzene was poor. and diallyl phthalate, and from 80 to 20 parts by weight rm A i TABLE 1 Gel polymer: ED'VIA EDMA EDMA EDMA E M TDMA DEDMA TEDMA DVB DVB DVB DAP 1 D Cmsslmkmg agent a. 0 5.0 7. 0 C 4. o 4. 5 5. 0 4. 0 5. 0 5.0 5. 0 5. 0 7. 0

P98 Monomer composition CP CP GP CBIgJ; CP GP OF UP GP CP CP GP D n-Dodecylmercaptan 0. 2 0. 3 0.35 0. 25 0. 25 0. 25 O. 25 0. 25 0. 3 0.3 0.3 0. 3 Conversion 90 98 97 93 90 91 95 93 80 90 95 80 Crosslinkiing densityXlO- 10. 7 25.0 31. 3 13.5 14. 6 17. 2 30. 4 22. 7 2. 4 8.2 22. 0 4. 2 S01 polymer:

Monomer composition OF UP CP CP g CP CP OF C1 C1 CP CP Mooney viscosity ML 1+4 (100 C.) 25. 5 22. 5 20. 0 24. 5 23. 0 23. 0 21. 0 23. 0 23. 0 22. 5 24. 5 21. 0 Gel polymer/sol polymer blend l'atil) 54/46 52/48 51/49 54/46 53/47 54/46 52/48 54/46 50/50 50/50 50/50 50/50 Mooney viscosity of blend ML +4 (100 C.) 48. 5 49. 5 51. 5 50. 5 51. 5 49. 0 48. 5 51. 0 49. 0 50. 5 48. 5 51. 0 Compound:

Extrusion rate, ccJsec.

(X 28. 2 39. 8 37. 1 31. 4 37. 5 35. 3 36. 1 35. 4 20. O 27. 0 28. 9 24. 5 Die swelling- 1. 27 1. 07 1. 05 1. 1. 26 1. 13 1.12 1. 18 1. 60 1. 35 1. 10 1. 52 Surface smoothne Exc. Exc. Exc. Exc. Exc. Exc. Exc. Exc. Good Exc. Exc. Exc.

gotes: *W h of Yb) a toluenesolfible 351 polymer obtained by X? polymerizing chloroprene or a mixture of chloroprene EDMA. Ethylene glycol dimethacrylate with a small amount of at least one copolymerizable TDMA: Tetramethylene glycol dimethacrylate monomer.

DEDMA: Diethylene glycol dimethacrylate TEDMA: Tetraethylene glycol dimethacrylate CPL Chloroprene 2.3DCBD: 2,3-dichlorobutadienel .3

St: Styrene As evident from the Table 1, polychloroprene elastomers prepared using a gel polymer having a density of crosslinking of at least 2.4 X 10" are extrudable at high extrusion rates without difficulty. The extruded product is characterized by a smooth surface. The elastomer prepared using a gel polymer of a crosslinking density of 0.6 X 10', which is outside the scope of the present invention, has poor extrusion characteristics.

What is claimed is:

l. A polychloroprene elastomer consisting of a blend of from 20 to 80 parts by weight of (a) a toluene-insoluble gel polymer, having a crosslinking density of at least 2.4 X 10' obtained by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer to a monomer conversion of at least 80 percent in the presence of a crosslinking agent selected from the group consisting of a compound represented by the formula;

2. An elastomer as in claim 1, wherein the cross-linking agent is diethylene glycol dimethacrylate or tetraethylehe glycol dimethacrylate.

3. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is one selected from the group consisting of styrene, vinyltoluene, butadiene, isoprene, 2,3-dichlorobutadiene-l ,3, methyl vinyl ketone, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and acrylonitrile.

4. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is styrene.

5. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is 2,3-dichlorobutadiene-l ,3.

6. The polychloroprene elastomer of claim 1 wherein the weight ratio of said gel polymer to said so] polymer varies from 50:50 to 54:46.

7. The polychloroprene elastomer of claim 1 wherein the Mooney viscosity (ML at C of the blend varies from 30 to 70. 

1. A polychloroprene elastomer consisting of a blend of from 20 to 80 parts by weight of (a) a toluene-insoluble gel polymer, having a crosslinking density of at least 2.4 X 10 6 obtained by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer to a monomer conversion of at least 80 percent in the presence of a cross-linking agent selected from the group consisting of a compound represented by the formula; wherein n is an integer of from 2 to 4, divinylbenzene and diallyl phthalate, and from 80 to 20 parts by weight of (b) a toluene-soluble sol polymer obtained by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer.
 2. An elastomer as in claim 1, wherein the cross-linking agent is diethylene glycol dimethacrylate or tetraethylene glycol dimethacrylate.
 3. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is one selected from the group consisting of styrene, vinyltoluene, butadiene, isoprene, 2,3-dichlorobutadiene-1,3, methyl vinyl ketone, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and acrylonitrile.
 4. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is styrene.
 5. An elastomer as in claim 1 in which the monomer copolymerizable with chloroprene is 2,3-dichlorobutadiene-1,3.
 6. The polychloroprene elastomer of claim 1 wherein the weight ratio of said gel polymer to said soL polymer varies from 50:50 to 54:46. 